Various block polymer compositions are known in the art. For example, triblock polymers such as the PCL-PEG-PCL and PLA-PEG-PLA triblock polymers comprised of polyethylene glycol (PEG) and poly(ε-caprolactone) (PCL), and polylactide (PLA) are disclosed by Cha et al., U.S. Pat. No. 5,702,717 and Lui et al. (Thermoreversible gel-sol behavior of biodegradable PCL-PEG-PCL triblock copolymer in aqueous solutions, J. Biomed. Mater. Res. B. Appl. Biomater., January, 2008, 84 (1) 165-75). The individual polymers forming the block polymer are all well-known, FDA-approved, biodegradable, and biocompatible materials.
In addition, the pentablock co-polymer PLA-PCL-PEG-PCL-PLA has been studied by Deng et al. (Synthesis and Characterization of Block Polymers of ε-Caprolactone and DL-Lactide Initiated by Ethylene Glycol or Poly (ethylene glycol), J. Polymer Sci., 1997, Vol 35 No. 4 703-708); Kim et al. (The Synthesis and Biodegradable behavior of PLA-PCL-PEG-PCL-PLA Multi Block Copolymer, Polymer Preprints, 2000, Vol. 49 No. 7 1557-1558). These insoluble polymers were proposed as tissue scaffolds by Huang (Polymeres Bioresorbables Derives de Poly(ε-caprolactone) en Ingénierie Tissulaire, Centre de Recherche surles Biopolyméres Artificiels, UMR CNRS 5473 Faculté de Pharmacie, Université Montpellier I en collaboration avec Division de Bioingénierie, Université Nationale de Singapour).
Pentablock co-polymer compositions described to form nanoparticles with a bioactive agent are disclosed by U.S. Pat. No. 8,551,531, PCT Publication No. WO2014/186669, and Patel et al. (Novel Thermosensitive Pentablock Copolymers for Sustained Delivery of Proteins in the Treatment of Posterior Segments Diseases, (2014) pp. 1185-1200), all of which are incorporated herein by reference. However, currently available compositions are typically only compatible with either hydrophobic or hydrophilic active agents, not both. Furthermore, hydrophobic active agents and combinations of hydrophilic and hydrophobic active agents can be difficult to formulate, in particular in the form of clear, aqueous solutions. Therefore, a need exists for improved aqueous formulations that can deliver various active agents to patients in need thereof.